The state of the art mentions various types of switching devices used to improve power factor. Their aim is to reproduce the input voltage at the power supply input, and to keep the current in phase with the voltage. The full-wave rectified voltage in a 50 or 60 Hz power line fluctuates between 0 volt and a peak value, indicating that the supplied current value should also be sinusoidal between 0 A and a peak value.
A boost topology is used with a flow converter coupled in series or another converter topology with potential separation. This approach has the disadvantage of being chopped in two phases. Also, connecting two switching power supplies in series is both expensive and energy inefficient, as the inefficiencies of both power supplies are multiplied. Furthermore, the boost topology with an interconnected push-pull transformer phase employs a one-phase concept.
The state of the art also mentions another topology, SEPIC (single-ended primary inductance), which can transform upward from 0 volt (flux voltage) to any desired voltage.
The above mentioned switching topology attempts to replace the booster with SEPIC topology. Still, the negative aspect of the two stage concept remains. Another disadvantage of boost topologies is the susceptibility of the intermediate circuit condenser to short circuits, the switching configuration itself being prone to shorts.
There is also a known regulating concept for boost topology in which a direct current ("dc") intermediate circuit voltage is generated in the sinusoidal line by a voltage-regulating amplifier whose amplified voltage error differential is multiplied by the type of input voltage and divided by the square of the average input voltage. This figure is then used as the reference current value.
State of the art industrial, telecommunications, and on-board aircraft supply circuits are subject to secondary malfunctions. System users who work with these supply circuits not only have to take steps against these naturally occurring malfunctions (e.g., lightning) but also against those caused by other circuit users.
A significant shortcoming of almost all supply circuits are fluctuations in static rated input voltage of up to .+-.40% (EN50 155) or vehicles using 12V (24V) which disrupt on-board circuits by up to &lt;6.5V (9.5V), depending on the type of power line or battery. The connected electronic systems or power supplies cannot handle these current fluctuations, resulting in malfunctions.
A particular problem of this type involves secure voltage supply for relays and contactors, and secure voltage supply for current-proportional hydraulic and pneumatic throttles and/or for blowers (known as loads). Since there is no guarantee that electro-mechanical switching components such as relays and contactors will switch or remain switched below a minimal input voltage due to their physical, magnet, and mechanical limits, fluctuations of supply voltage leads to malfunctions. The state of the art recommends monitoring supply voltages with monitoring switches. Reaction is impossible in emergency scenarios such as too low input voltage due to load disconnection, long leads, or less than ideal feed sources. Substantial improvements in contactors are being made to insure that they switch properly even with fluctuating input voltages. Still, these improvements involve substantial costs.
It is also a known fact that in a switched-on state, loads such as contactors can be operated at voltages higher than their rated voltages, resulting in substantial power loss. During power line over-voltage, contactors can be destroyed or their service life shortened. Intentionally or not, this would result in unpredictable changes in blower RPM and torque.
According to the state of the art, servo or AGC amplifiers are used to drive current proportional throttles. These amplifiers may be fed by power transformers and controlled linearly or chopped on a rated voltage UN. However, such solutions are extremely expensive. Also, when boosters are used, the output voltage cannot be set at or adjusted to the power line's rated voltage.
During transistor defects, step-down boosters are switched through to the input voltage at the output. For step-up boosters, cutting the input voltage creates a dynamic short circuit in the output condenser, and the circuit is not protected against shorts. EP 0 388 069 A2 describes a dc/dc converter switching circuit. Essentially, the converter consists of a ladder-like circuit structure in which the horizontal components include an inductance L1, a capacitance C2, and a diode D1, and the vertical components comprise a transistor S1, an inductance L2, and a capacitance C3. The circuit configuration is characterized by containing only one transistor connected to the circuit group, and the transistor requires only one control signal. The circuit configuration also requires no isolating transformer. The above contains no indications as to PFC rating or control behavior.
"Using SEPIC Topology for Improving Power Factor in Distributed Power Supply Systems" by J. Sebastian et al., in EPE Journal, vol. 3, no. 2, June 1993, describes the use of a PFC rated SEPIC topology as power supply system. A multiplication method is proposed to regulate PFC, while a voltage sequence method is suggested which can be applied in various operating phases (continuous control operation or intermittent dc flow). Especially in the multiplication method, a sinusoidal input voltage UE, an input current IE, and an output voltage UA are input into the regulator circuit as actual values. No rating or processing is provided for the output current IA. The input current IE fluctuates along with the input voltage, which has a lasting effect on regulation behavior. Further, the formula used to calculate PFC rating for (step-up) boosters is applied.
Another SEPIC topology can be found in Wen-Jian Gu, et al's article "Topologies and Characteristics of DC--DC Converters Using Class E Resonant Switch (sic)," Electronics and Communications in Japan, Part I, vol. 75, no. 1, 1992, pp. 82-96. PFC regulating circuits are not mentioned in this article as they relate to SEPIC topology.